What do we know about HS2?
The government is planning a new high-speed rail network, from London to Birmingham and to Manchester and Leeds, known as HS2.
Ministers say it will improve the transport network and boost the economy, but there has been controversy about the exact route of the line and its effect on those living near it. Here are the key points that we know so far.
What is HS2?
The initial plan is for a new railway line between London and the West Midlands carrying 400m-long (1,300ft) trains with as many as 1,100 seats per train.
They would operate at speeds of up to 250mph - faster than any current operating speed in Europe - and would run as often as 14 times per hour in each direction.
This would be followed by a V-shaped second phase taking services from Birmingham to Manchester and Leeds.
The Department for Transport says there will be almost 15,000 seats an hour on trains between London and the cities of Birmingham, Manchester and Leeds - treble the current capacity.
What will the second phase involve?
In November 2016, the government confirmed the route for the second phase - from Crewe to Manchester and the West Midlands to Leeds.
A new HS2 station will be built next to Manchester Piccadilly, with a spur to take HS2 to another new station at Manchester Airport.
And in July 2017, the government said the line's north-eastern route, to Leeds, will run east of Sheffield, with some trains going into the city via a new spur and existing lines.
The Department for Transport said the full line would eventually connect Birmingham, Manchester, Liverpool, Leeds, Sheffield and the East Midlands in a Y-shaped network, with all of them being linked to London.
When will it open and how much will it cost?
The first phase of the £56bn railway is due to open in December 2026, with trains to travel at high speed between London and Birmingham before continuing on the existing West Coast Main Line.
But earlier this year, the Public Accounts Committee cast doubts on this deadline. calling it "overly ambitious".
The onward legs to Manchester and Leeds could start being built in the middle of the next decade, with the line open by 2032-33.
In June 2013, the government revised the cost of the project upwards, due to an increase in the amount of tunnelling required on the route. This took the estimated budget from £32.7bn to £42.6bn at present values - with the cost of phase one increasing from £16bn to £22bn.
Could the HS2 project be delivered quicker?
The scheme's chairman, Sir David Higgins, said building work on the northern section should be accelerated to reach as far as Crewe by 2027, instead of aiming for Birmingham by 2026.
In a report for the government, called HS2 Plus, he said the second phase of HS2 could then be completed by 2030 instead of 2033.
Sir David also called for a more comprehensive development of HS2's London hub, Euston station.
What does HS2 mean for passengers?
The Department for Transport says the project will cut Birmingham-London journey times from 1hr 21min to 49min.
Once the second phase is complete, Manchester-London journeys would take 1hr 8min (down from 2hr 8min), and Birmingham-Leeds 57min (down from 2hr). This would effectively reduce journey times between London and Edinburgh and Glasgow by an hour to 3hr 30min.
The government believes its creation will free up capacity on overcrowded commuter routes. It also estimates the new line could transfer 4.5 million journeys a year from the air and nine million from the roads, reducing the number of lorries on busy routes.
What about fares?
There has been no announcement on ticket prices. The government says its proposals "assume a fares structure in line with that of the existing railway" and that HS2 could generate sufficient demand and revenue without needing to charge premium fares. It estimates total fare revenues of up to £34bn over a 60-year period.
Who are the winners...
- Old Oak Common in north-west London will be transformed from a rail depot to a 14-platform interchange station and will provide fast connections to central London, the City and Heathrow airport. The government expects the station to support some 20,000 new jobs
- The northern cities served by the new line, which will be better connected to each other and to the south of England
- Commuters on the West Coast Main line. Network Rail estimates the line will be full by 2024 and it's hoped HS2 will significantly reduce the strain
- Places further away from the line, like Wales, aren't expected to see any economic benefits and could lose jobs as a result
- Butterflies, bats and birds. The Wildlife Trusts say both phases directly affect nature reserves and wildlife sites which could lead to a net loss in biodiversity
- The Chilterns, Buckinghamshire and Oxfordshire - here, historic buildings are at risk of damage or demolition, and remaining residents will face noise pollution
- Some residents in Mexborough, South Yorkshire, will lose their homes. Sixteen of 216 homes on a housing estate in Mexborough will be demolished
- Thousands of people living in Camden, north-west London, face years of disruption during phase one. Parts of the Regent's Park Estate will also be demolished
Why are ministers so keen on the scheme?
The government argues that Britain's rail network is reaching capacity, while infrastructure owner Network Rail says the southern section of the West Coast Main Line - currently the quickest rail route between London and Birmingham - will be "effectively full" by 2024.
Ministers claim the London-West Midlands section alone will create around 40,000 jobs.
Groups such as the Campaign for High Speed Rail say there will be added knock-on benefits, while some MPs believe it could be a catalyst for economic growth and help rebalance the economy between the North and South.
What about opposition to HS2?
HS2 will pass through around 70 parliamentary constituencies, and local groups opposed to the scheme are lobbying their MPs to vote against the plans.
There is political pressure on some Conservative MPs in particular, who will see the route pass through their constituencies, and some have indicated that they may vote against the government's bill when it reaches Parliament.
Pressure group Stop HS2 argues that England's north and Midlands will actually lose out to London, rather than benefit, and that projections for its success do not take into account competition from conventional rail.
Stop HS2 believes that once the high-speed railway is operating, existing intercity services to London will be reduced by up to two trains an hour.
HS2 Action Alliance claim more than 70% of the 30,000 jobs created around HS2 stations in phase one will be in London rather than the West Midlands.
Others object on the grounds that it will cut through picturesque countryside, impacting areas of natural beauty and the ecosystems they support.